plotter: Enable user specified arg forwarding to matplotlib
plotter: Enable user specified arg forwarding to matplotlib

This change allows the user to register args for forwarding to
matplotlib and also unregister the same.

Change-Id: If53dab43dd4a2f530b3d1faf35582206ac925740
Signed-off-by: Kapileshwar Singh <d373e2b6407ea84be359ce4a11e8631121819e79@arm.com>

bjackman/trappy,ARM-software/trappy,joelagnel/trappy,JaviMerino/trappy,joelagnel/trappy,JaviMerino/trappy,joelagnel/trappy,sinkap/trappy,derkling/trappy,sinkap/trappy,ARM-software/trappy,derkling/trappy,joelagnel/trappy,sinkap/trappy,JaviMerino/trappy,bjackman/trappy,derkling/trappy,sinkap/trappy,ARM-software/trappy,ARM-software/trappy,bjackman/trappy,bjackman/trappy